A LINEAR RFQ TRAP FOR COOLING AND BUNCHING OF RADIOACTIVE ION BEAMS Ari Jokinen University of Jyväskylä CERN / PS-division Introduction RFQ Buffer gas cooling JYFL ion cooler and buncher

WHY BEAM COOLING ? dx q dq x cooling Emittance: characteristic property of an ion beam for a given number of ions, want minimum beam size, divergence and energy spread (hence, small emittance) Ion beam geometry Phase space diagram dx q dq x Liouville’s theorem: area of dx by dq is constant small divergence - large beam small beam spot - large divergence therefore to reduce emittance we need a dissipative environment: cooling

COOLING TECHNIQUES Storage rings: stochastic cooling electron cooling laser cooling Ion traps: resistive cooling evaporative cooling laser cooling buffer gas cooling (fast, universal -> optimal technique for RIB)

BUFFER GAS COOLING Two initial energy regions: A. Elastic collisions, Eion >> Egas collision rate energy loss in single collision B. Viscous damping, Eion » Egas Origin: long-range interaction between incoming ion and polarized buffer gas atoms -> viscous drag Ions are damped to zero (in the model) In reality: RF-heating, thermal movement, ...